Speaking to The Times in 2002, Mr. Ratner said: “A permanent war abroad means permanent anger against the United States by those countries and people that will be devastated by U.S. military actions. Hate will increase, not lessen; and the terrible consequences of that hate will be used, in turn, as justification for more restrictions on civil liberties in the United States.”

Michael Ratner, a fearless civil liberties lawyer who successfully challenged the United States government’s detention of terrorism suspects at Guantánamo Bay without judicial review, died on Wednesday in Manhattan. He was 72.

The cause was complications of cancer, said his brother, Bruce, a developer and an owner of the Brooklyn Nets.

As head of the Center for Constitutional Rights, Michael Ratner oversaw litigation that, in effect, voided New York City’s wholesale stop-and-frisk policing tactic. The center also accused the federal government of complicity in the kidnapping and torture of terrorism suspects and argued against the constitutionality of warrantless surveillance by the National Security Agency, the waging of war in Iraq without the consent of Congress, the encouragement of right-wing rebels in Nicaragua and the torture at the Abu Ghraib prison during the Iraq war.

“Under his leadership, the center grew from a small but scrappy civil rights organization into one of the leading human rights organizations in the world,” David Cole, a former colleague at the center and a professor at Georgetown Law School, said in an interview this week. “He sued some of the most powerful people in the world on behalf of some of the least powerful.”

Mr. Ratner, who majored in medieval English at Brandeis University in the 1960s, was radicalized by the teachings of the New Left philosopher Herbert Marcuse and the preachings of a classmate, Angela Davis. He moved further to the left as a law student at Columbia University when he witnessed police brutality after students seized campus buildings in 1968. He defied legal odds and even occasional death threats to defend lost causes, gambling that even a verdict against his clients could galvanize public opinion in his favor.

“He was part of a generation of lawyers that was absolutely bold and that understood the political aspects of law,” his former wife, Margaret Ratner Kunstler, a civil rights lawyer, said this week, “and that was not afraid of bringing a lawsuit that was going to lose if it was going to support the community.”

Professor Cole predicted that Mr. Ratner would be best remembered for filing the first lawsuit on behalf of Guantánamo detainees in a case that eventually affirmed their right to judicial review.

“This was a case that was regarding a fundamental principle, going back to the Magna Carta in 1215, about the right to have some kind of a hearing before you get tossed in jail,” Mr. Ratner told Mother Jones magazine in 2005.

In 2008, the Supreme Court ruled 5 to 4 that prisoners at Guantánamo, where the court said the American government exercised de facto sovereignty, had a constitutional right to habeas corpus, which they had been denied under the Military Commissions Act.

Professor Cole said Mr. Ratner’s tenacious advocacy not only gave the detainees the right to their day in court, but also culminated in “the first Supreme Court decision in history to rule against a president in wartime regarding his treatment of enemy fighters.”

While Guantánamo still has not been closed, as President Obama had promised, hundreds of detainees have been released.

“When I asked him, several years later, what he thought his chances were in filing that suit,” Professor Cole recalled, “he answered: ‘None whatsoever. We filed 100 percent on principle.’ That could be his epitaph.”

Michael David Ratner was born in Cleveland on June 13, 1943. His father, Harry, was a Jewish immigrant from Russia who ran a building supply company. His mother, the former Anne Spott, was a secretary and helped resettle refugees after World War II, during which scores of the couple’s relatives were killed in the Holocaust.

Michael Ratner’s college radicalism had deep personal roots. His father once gave shoes to a homeless man who came to the door seeking a handout. His mother refused to enter a Florida airport because it was racially segregated.

Mr. Ratner recalled in an interview with The New York Times in 2002 that as a boy he had dreamed of becoming an archaeologist, adding: “I used to think it wasn’t political, but it turns out to be highly political. After all, what layer of civilization do you save?”

After graduating in 1966 from Brandeis, where he met Professor Marcuse and Ms. Davis, he earned a degree from Columbia Law School (after taking a year off to work for the NAACP Legal Defense and Educational Fund on a Baltimore school desegregation case). He then clerked in Manhattan for Judge Constance Baker Motley, the first black woman to serve on the federal bench.

In 1971, he joined the Center for Constitutional Rights, a nonprofit organization with headquarters in Manhattan, which litigates civil and human rights cases and was co-founded in 1966 by William Kunstler, whom Mr. Ratner’s first wife later married.

Mr. Ratner’s first case with the center involved a suit on behalf of inmates killed and injured at the Attica Correctional Facility in upstate New York after a bloody uprising there in 1971, although the court ruled that it could not compel prosecutors to indict prison guards or the state troopers for their actions.

He was the center’s legal director from 1984 to 1990 and its president from 2002 to 2014. He was also president of the National Lawyers Guild and of the European Center for Constitutional and Human Rights, and founded Palestine Legal, which defends protesters on behalf of Palestinian rights.

Mr. Ratner defended Julian Assange and WikiLeaks for disseminating millions of secret American government documents; served as a counsel to Jean-Bertrand Aristide, the Haitian president, in the prosecution of war crimes; and advocated on behalf of Haitian refugees held at Guantánamo after the 1991 coup that overthrew Aristide, the country’s first democratically elected president.

He is the author of “The Trial of Donald Rumsfeld: A Prosecution by Book, Against War With Iraq” (2008) and “Guantánamo: What the World Should Know” (2004).

“He felt very much that torture doesn’t make us safer, and that everyone needs a defense,” Ms. Ranucci said.

Speaking to The Times in 2002, Mr. Ratner said: “A permanent war abroad means permanent anger against the United States by those countries and people that will be devastated by U.S. military actions. Hate will increase, not lessen; and the terrible consequences of that hate will be used, in turn, as justification for more restrictions on civil liberties in the United States.”

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